1. Field of the Invention
This invention relates to a bending machine to wind a strip or the like into a spiral. Usually, a spiral-bending machine has a mandrel supporting a bending tool designed to receive and retain an end of a strip or the like to be bent and at least a supporting or counteracting element of a strip to allow its permanent deformation. Here and below the term of "mandrel" means in proper sense the shaft transmitting the movement to a workpiece.
2. Description of the Related Art
In a known spiral bending machine, the bending tool consists generally of a circular plate rigidly supporting on its external side a projection shaped according to a portion of spiral. In order to obtain a spiral, for example, of three turns, therefore a complete set of bending tools of the above mentioned type is necessary, comprising for example a first bending tool for the first turn near the pole, a second bending tool for the second tool and so on. A roller of a supporting and counteracting element rigidly supported to the machine table is operatively connected to the first bending tool, while a second roller, being part of the same supporting element but fitted on the table in a diametrically opposed position, is connected to the second bending tool. Just the same for the third turn. Naturally this kind of spiral-bending machine requires, for making only three turns, that three bending tools are fitted on and removed from the mandrel and correspondingly the supporting and counteracting element is fitted on and removed from three different positions on the machine table. In addition to a waste of time, one must consider that the operation needs of a certain capacity by a worker. He must estimate correctly in which point he has to stop the bending operation by means of a bending tool and continue it by means of a subsequent bending tool without suffering from problems of interference of the workpiece already partially bent by the bending tool useful for carrying on the spiral machining. In another spiral-bending machine known the bending tool consists of a first bending tool member connected to a mandrel, acting as a grip element for the strip to be bent, and of second bending tool member able to be arranged continuously with the first bending tool member to form a complete turn or a little more. The second bending tool member is shaped "as a comma", having a thickened portion, through which it is pivoted on the first bending tool member, and thinning with an arc toward the free end. The second bending tool member is provided in various conformations, to which different patterns of the portion of spiral obtainable correspond. As a whole, the bending tool of this second spiral-bending machine is not so rigid to allow metal workpieces of different material and thickness to be worked in a same satisfactory way, unless the worker runs the risk of breaking the bending tool. Further, such a bending tool enables the spiral-bending for a little more than a turn, as it is not possible to add other elements overhanging on the second bending tool member.